Oxypropylene polymers having a reactive silicon group(s) are polymers which are capable of becoming liquid polymers and are cured in the presence of moisture at room temperature to form rubbery elastic cured articles. Accordingly, these polymers are used in the fields of elastic sealants and adhesives.
It is desirable that these polymers have an appropriate viscosity when blended or applied. Further, it is desirable that these polymers have a given molecular weight to provide cured articles having desired mechanical characteristics, particularly rubber elasticity high in flexibility.
Many methods for preparing organic polymers having a reactive silicon group(s) in the molecule have been proposed. For example, organic polymers (trade mark: MS polymer) having a main chain composed of an oxypropylene polymer and methoxysilyl groups at chain terminal positions are manufactured by Kanegafuchi Kagaku Kogyo K.K. and are commercially available.
However, there is conventionally a difficulty in manufacturing oxypropylene polymers having a narrow molecular weight distribution (Mw/Mn ratio measured by GPC is small) and a high molecular weight. Accordingly, only polymers having a wide molecular weight distribution (Mw/Mn measured by GPC is large) including oxypropylene polymers having reactive silicon group(s) have been conventionally used. These polymers have a relatively high viscosity.
It has recently been reported that an oxypropylene polymer having a narrow molecular weight distribution has been obtained [see, JP-A-1-229035 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-B-46-27250 [the term "JP-B" as used herein means an "examined Japanese patent publication")]. Polymers having a main chain composed of an oxypropylene polymer having a narrow molecular weight distribution and reactive silicon groups, as terminal groups, introduced into the terminal positions of the polymer chain, have a low viscosity before curing.
The present inventors have found that when both (an oxypropylene polymer having a wide molecular weight distribution and an oxypropylene polymer having a narrow molecular weight distribution) are mixed, the viscosity of the oxypropylene polymer having a wide molecular weight distribution can be greatly lowered without reducing the excellent rubber elasticity of cured articles, and hence there can be efficiently solved a problem with regard to a high viscosity of the oxypropylene polymer having a wide molecular weight distribution and which is conventionally unfavorable to practical use. The present invention has been accomplished on the basis of this finding.